The invention relates to peristaltic devices, and particularly to a variable occlusion peristaltic device that provides a constant occluding pressure.
Peristaltic devices are commonly used as pumps for pumping a fluid while keeping the fluid isolated from potential contaminants. Such peristaltic pumps find application in medicine, food, and pharmaceutical processing, and in painting or coating systems. Peristaltic devices are also employed as meters for metering the volume of fluid flow through a conduit and as motors for turning a shaft.
Regardless of the particular application, peristaltic devices include generally a housing with an arcuate roller or occlusion track defined therein and a rotor mounted in the housing for rotation about the longitudinal axis of the roller or occlusion track. A number of occluding members or rollers are mounted on the rotor and adapted to engage and compress a resilient and flexible tubing contained in the roller or occlusion track.
When used as a pump, for example, a motor is connected to drive the rotor about its rotational axis. As the rotor rotates, the rollers or other occluding members are repetitively brought to bear against the tubing extending through the housing, compressing or collapsing the tubing against the occlusion track, and urging the fluid or other material contained in the tubing forward in the direction of the occluding member motion relative to the tubing. The occluding members could be used to partially collapse the tubing or to completely collapse the tubing, in the latter case forming isolated slugs of fluid in the tubing between occluding members.
There were a number of problems associated with prior peristaltic devices, some problems being accentuated by the particular desired function of the device. First, the tubing upon which the peristaltic device operated had to be looped or loaded through the housing in order for the device to operate, and such loading was difficult where the occluding members remained in a fixed occluding position in the housing. Thus, there has been a need for means of varying the position of the occluding members quickly, particularly from a remote location. Also, prior peristaltic devices were not capable of maintaining a constant occluding force on the tubing during operation, regardless of the pressure of the fluid passing through the tubing. Finally, where the peristaltic device was to be used in a controlled clean environment, the preferred variable occluding force had to be applied without the use of potentially contaminating material such as hydraulic fluid.
U.S. Pat. No. 4,720,249 to KREBS et al. is directed to a peristaltic pump with enhanced tube loading features. KREBS et al. show several different mechanisms for varying the position of the occluding members of a peristaltic pump from an extended occluding position to a retracted loading position. In the retracted position, all of the occluding members were withdrawn inwardly into a centrally positioned rotor away from the occlusion track so as to provide room for inserting or withdrawing the tubing. In one preferred form of the KREBS et al. device, a hydraulic system contained in the rotor was used to control the position of the occluding rollers.
Although KREBS et al. do disclose means for withdrawing occluding members for purposes of loading and unloading tubing, the position of the rollers could not be controlled remotely. Furthermore, the hydraulically operated variable occlusion system required hydraulic fluids which are undesirable for use in certain controlled environments. Also, the KREBS et al. variable occlusion system did not provide a constant occluding force on the tubing during operation. Once the KREBS et al. rollers were hydraulically set in the extended position, any change in the pressure of the fluid in the tubing changed the force applied between the occluding members and the tubing. Finally, the KREBS et al. device did not enable the occluding force to be increased or controlled while the pump was operating to ensure that the tubing remained completely collapsed.